Objection 1: It would seem that grace is not a quality of the soul. For no quality acts on its subject, since the action of a quality is not without the action of its subject, and thus the subject would necessarily act upon itself. But grace acts upon the soul, by justifying it.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic action quality
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“And hence the remission of sins does not take place without some effect divinely caused in us, as will appear later (Q. 113, A. 2). ________________________
SECOND ARTICLE [I-II, Q. 110, Art. 2]
Whether Grace Is a Quality of the Soul?
Objection 1: It would seem that grace is not a quality of the soul. For no quality acts on its subject, since the action of a quality is not without the action of its subject, and thus the subject would necessarily act upon itself. But grace acts upon the soul, by justifying it. Therefore grace is not a quality.
Obj. 2: Furthermore, substance is nobler than quality. But grace is nobler than the nature of the soul, since we can do many things by grace, to which nature is not equal, as stated above (Q. 109, AA. 1, 2, 3).” source